Consider further aortic valve intervention for patients with a significant increase in trans-prosthetic gradient or severe regurgitation, taking account of their degree of symptoms and relative surgical or interventional risk.

Perform repeated TTE assessment annually or sooner if new symptoms occur, and carefully compare findings with previous examinations in the same patient.

Report any incidents of prosthetic valve failure to the manufacturer and to MHRA or devolved administration (see enquiries section below).

Action by

Cardiologists and cardiothoracic surgeons responsible for the follow-up of patients implanted with biological replacement aortic valves.

Deadlines for actions

Actions underway: 10 May 2017

Actions complete : 11 August 2017

Device details

The Sorin Mitroflow LX aortic biological prosthetic replacement valve: sizes 19 and 21mm.
(LivaNova were previously known as Sorin Group up to October 2015)

All lot numbers and all serial numbers are affected by this alert.

Problem/background

This alert applies only to the Mitroflow ‘model LX’ valve which was marketed in the UK by Sorin between 2005 and 2014. Patients implanted with the smaller sizes of the Mitroflow LX model are more prone to early SVD (especially younger patients) and therefore should be prioritised for extra surveillance. It is estimated that less than 80 of these smaller sized valves have been sold in the UK in the last five years (and less than 1,300 in the last 10 years). Hence even allowing for some implants having taken place later on within their 5-year expiration period, the number of affected patients is expected to be comparatively low.

An earlier version, the ‘model 12’ Mitroflow valve is not included in this alert, because it was last distributed in the UK in 2006. With a maximum shelf-life of 5 years, these valves will have been implanted no later than 2011, and so should already be subject to the increased surveillance recommended for all prosthetic valve patients from 5 years, in accordance with the European Society of Cardiology Guidelines. This alert essentially brings forward these follow-up recommendations to apply to all patients with the smaller size Mitroflow LX valve.

The more recent version of the Mitroflow valve, the ‘model DL’ is not included in this alert, because there is currently no evidence that it is affected by a higher than expected incidence of early SVD. This may be linked to the introduction of a phospholipid reduction treatment for this model to reduce calcification. We intend to review the safety and performance of model DL once more clinical data becomes available.

The recommendations in this alert are based on our review of a number of published papers on the Mitroflow series valves over the last few years in which we noted some consistent findings giving rise to concerns. In general, the concerns relate to a higher risk of SVD in patients with the smallest aortas, particularly in the presence of patient-prosthesis mismatch (PPM). Some of the more significant references and observations are listed below:

A 2016 report by the National Institute for Cardiovascular Outcomes Research (NICOR), which used data from all National Health Service and private hospitals in England and Wales that submitted to the National Adult Cardiac Surgery Audit (NACSA) between 1998 and 2013. The report highlighted that the Sorin Mitroflow series displayed a larger hazard than expected with the 10-year overall freedom from re-intervention or death rate for the Mitroflow valve found to be 33.8%, compared with the overall average of 47.2% for all non-Sorin biological valves.

A 2014 report by the Odense University Hospital, Denmark3, revealed an increased risk of mortality and/or reoperation for Mitroflow valves VS a comparator valve.

A 2014 report by the Nantes University Hospital, France4 presented early SVD as frequent in Mitroflow valves (models 12A/LX), especially for small sizes (19 and 21 mm) with reduced overall survival.

In response to the concerns raised by MHRA, the manufacturer is planning a targeted, post-market surveillance study in the UK to compare Mitroflow with all-comers, including the use of other stented tissue valves that require ancillary procedures such as aortic root enlargement. Over time this study intends to use existing NHS data, as well as data from the Hospital Episodes Statistics and Office for National Statistics to provide a more complete assessment of this SVD signal.

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